Abstract : The report documents the design, construction, and data reduction techniques of a balloon borne ultraviolet Ebert-Sekera spectrophotopolarimeter, whose purpose is to measure the natural sky backgrounds at altitudes greater than 100,000 feet. Considerable detail has been spent in describing the various mechanical, electrical and optical components of the system to serve as a guide for future improvements and alterations of the instrument. The data reduction section describes the various computer programs that have been necessary in order to reduce the large amount of data that is obtained. Intensity data at altitude has not been obtained as of yet, but the system has been shown to be capable of giving intensity and the Stokes parameters of the incident light. (Author)